Studies on Multifunctional Block Copolymers for Holography

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Novel photorefractive (PR) block copolymers consisting of photoconductive and electro-optically(EO) active blocks were synthesized via the atom transfer radical polymerization (ATRP) of acrylates with cyanobiphenyl (GB) unit followed by the polymerization of acrylate with carbazole(Cz) moiety. In DSC thermogram for block copolymer, two glass transition temperatures corresponding to those for both blocks were observed on the first run indicating that both blocks were microphase separated each other. By four-wave mixing (FWM) experiments for the polymers doped with electron accepting compounds, 25% of diffraction efficiency was observed at 80 V/μm. This value was much higher than that observed in statistical copolymer with the similar chemical composition. In two-beam coupling (2BC) experiments, rnmetri c energy exchange (gain coefficient of 100 cm^<-1>) was observed at 45 V/μm. Novel asymmetric succinate (TH-NVA) containing electron accepting thioxanthone and electron donating 4-(2-nitrovinyl)aniline derivative was synthesized. TH-NVA was found to readily form an amorphous glass when the liquid sample was cooled in air at room temperature. Differential scanning calorimetry revealed that the melting point of crystalline sample and the glass transition temperature of glassy sample are 130 and 44℃, respectively. Absorption tail in longer wavelength region was due to the charge transfer interaction between electron accepting and donating units. In two beam coupling experiments, TH-NVA showed asymmetric energy transfer (coupling gain ; 42cm^<-1>) without an external electric field.